1. Field of the Invention
The present invention relates to an automotive lighting fixture and more particularly a lighting fixture in which a lamp having a discharge bulb is integral with a lamp having an incandescent bulb.
2. Related Art
Application of lighting fixtures with a discharge bulb as a light source to automotive headlights is increasingly examined because such a discharge bulb has high luminescence efficiency, excellent color properties and a long life. However, a lighting fixture of the sort mentioned above needs a high voltage at which the discharge bulb causes electric discharge and a lighting circuit for raising a car battery voltage up to a desired level is required for the lighting fixture. Therefore, a lighting circuit unit forming a booster circuit, that is, a Starter circuit portion for raising the voltage up to the level required for the discharge bulb has been fitted integrally to part of a lighting fixture body.
In the case of a lighting fixture having combination structure in which a plurality of lamps are integrally installed, dimensions of reflectors and a lighting fixture body have been designed without consideration of the kinds of bulbs for use therein. When a headlight to be formed is of a combination lamp type wherein, for example, a lamp having a discharge bulb is used as a passing beam lamp (or low beam lamp) and a lamp having an incandescent bulb as a travel beam lamp (or high beam lamp), these lamps being integrally combined, the reflectors of the respective lamps are integrally formed in substantially the same dimension and contained in one lighting fixture body.
The reflectors of the respective lamps in such a conventional headlight have been formed in the same dimension and, though the luminance of the discharge bulb is extremely greater than that of the incandescent bulb, the luminous flux width of both of them is substantially the same because the reflective surfaces of the reflectors for the discharge and incandescent bulbs are similar. In consequence, a high degree of illumination is barely present at the peripheral portion of a light distribution area and the problem is that the light emission is not efficient. Light is particularly prevented by a shade in the passing beam lamp from being projected onto part of the area of the reflector, that is, the area where light is reflected upward in the reflector. Therefore, the effective area in which the reflector actually contributes to light reflection is much smaller than the whole area of the reflector and the amount of light irradiated by the passing beam lamp is small, thus reducing the visibility. In view of the fact that the use of passing beam lamps is continued while an automobile is traveling in urban districts, the reduced visibility is undesirable for safe driving.
Further, the heat produced by the discharge bulb is greater than that by the incandescent bulb in proportion to the luminance of the discharge bulb. Consequently, dissipation of the heat from the discharge bulb is required in consideration of the adverse influence of excessive heat on the reflector. However, no such measures have been taken so far. It should also be taken into consideration that the electromagnetic waves radiated from the discharge bulb affect a car radio and other electronic devices. Particularly, in a case where the lighting circuit for lighting the discharge bulb is arranged on the outer side of the lighting fixture body, the electromagnetic waves radiated from a lead connecting the lighting circuit and the discharge bulb are extremely strong and considerably affect electronic devices accordingly. As relatively large-sized electronic parts such as a booster transformer and capacitors are required in the lighting circuit, moreover, the whole lighting fixture also tends to become large-sized when the lighting circuit is attached to the outside of the lighting fixture body.